Descaling a reactor vessel without harming the lining that protects it

Project facts

Why descale a reactor in a plant that is winding down?

Decommissioning is not demolition — it is a controlled wind-down, and this plant still had production years ahead before its planned closure. A High Pressure Acid Leach facility precipitates mixed sulfide as part of its process, and years of operating with that scale had cost the reactor working volume and buried the baffle plates that keep its contents properly mixed. Baffles exist to break the swirl an agitator creates; buried under scale, the contents swirl instead of mixing, and the uneven loads feed back into the agitator shaft and its mechanical seal. The plant had accepted that trade because no available method could remove the scale without destroying the brick lining. To finish its remaining years at design condition — and ultimately hand the site back in original condition — the vessel had to come clean without losing the lining. Dezu arrived proven on exactly this deposit: our recurring shutdown program at an HPAL nickel refinery has removed mixed sulfide scale at every minor and major shutdown since 2023, and we had descaled an autoclave at this plant the same year. For the decommissioning campaign, the plant trialed us on a first reactor scope, then extended us to the full vessel.

What makes mixed sulfide scale hard to remove safely?

Three problems arrive together. The scale is hard and thick, so mechanical chipping takes forever. The work happens inside a confined vessel at elevated heights, so every added tool and hour is added risk. And the vessel walls are lined with acid-resistant brick that must survive the cleaning — the lining is the equipment's integrity, and impact tools that are aggressive enough to beat the scale are aggressive enough to break the bricks. Traditional descaling loses on all three at once: too slow, too dangerous, too damaging.

How did Dezu remove it without damaging the brick lining?

High pressure water attacks the deposit at the scale-to-brick interface without hammering the lining behind it — the same physics that lets hydro demolition strip concrete while preserving rebar, translated into a vessel. We proved the parameters on a trial scope first — the first sections of the vessel, against the real scale. The campaign then ran top-down, level by level, so falling scale, crew positioning, and energized water inside a confined space stayed controlled at every stage.

What did five months inside a reactor vessel teach us?

Water quality proved to matter as much as water pressure. Cavitation — the same collapsing-bubble energy that erodes scale — works on the contractor's own equipment too, and managing its effect on seals, packing, and metal parts became part of running the job. Nozzles and waterjet PPE wore at rates far beyond normal duty, so consumables planning became a production discipline of its own. These are the operating costs of doing months of ultra high pressure work inside a vessel, and knowing them in advance is part of what a client hires.

What was the result?

The reactor vessel was descaled through the full campaign — nine wall levels and the floor — with the brick lining intact: working volume restored, baffle plates re-exposed, the vessel fit to return to service for the plant's remaining production years and to meet the contractual hand-back standard. The engagement closed on schedule after five months — the proof point that hydro demolition equipment scales from a single repair to an entire decommissioning program.